If it involves sick or hurt or injured or even emotionally drained Dean, maybe try it at hoodie_time, though it's not actually a prompting-com.
If it's Sam who gets a bit battered (emotionally or physical), there's the ohsam com.

I also think there is something that's called "Supernatural plot bunnies", but I'm not sure if that's still active...

I've found a community called "SPN bunnies" but it has not been updated for a long time !
Thank you anyway.
:)